I have a 391 double feeding from the mag tube. It's not every time, but often enough. The gun functions fine if just loading the chamber and one in the mag tube. Removed / cleaned the bolt, trigger group. Cleaned and lubed the shell stop and confirmed it moves freely. I did not remove it from the receiver. This did not fix the problem. Cheap Federal shells and AA's would both double feed. Any thoughts on what to look for? Thanks.